Solid-state lighting such as those based on light emitting diodes will eventually replace most if not all of the conventional types of lighting that we have today. The main types in use in residential, commercial, and industrial settings are linear fluorescent, compact fluorescent, incandescent, and high intensity discharge. A major attraction of LED lighting is reduced energy costs due to greater efficiency of the technology. Other attractions are that they potentially have a much greater life span than the alternatives and do not contain hazardous chemicals such as mercury as do fluorescent bulbs that can contaminate the water supply when discarded and your house if you break one of the bulbs.
The main detractions with LED lighting today are the high cost of the lamps and in most examples available on the market that I have looked at, substandard performance. However, the technology is advancing at a rapid rate with the efficiency of the LEDs increasing about 84% per year at this time. This efficiency is now beginning to surpass linear fluorescent bulbs at around 100 lumen/watt but is still too expensive to compete well. As the price of LEDs comes down, the cost of the interface circuitry becomes relatively more important making this a timely invention.
Another negative is that the life of the lamps on the market is not reaching the 50K+ hours promised by the LED technology. This can be due to interface component failures such as large electrolytic capacitors that have a limited life that becomes even shorter as ripple current increases. It could also be due to LEDs being stressed by overheating, over voltage, or current spikes in excess of their maximum current rating.
Many companies are looking for a simple low cost method of creating an LED light that can be used with standard AC line voltages (110 VAC, 60 Hz or 220 VAC, 50 Hz). The methods currently available to interface LEDs to high voltages are expensive and require a large amount of area and volume inside of a light bulb or need a separate power supply similar to the ballast in a fluorescent lighting fixture to drive the light bulbs.
These methods typically use an AC to DC power supply with a step down transformer to reduce the voltage below 60 VDC thus accommodating the lower voltage semiconductors that are available for regulating the current supplied to the light. The light output of an LED is a direct function of the current flowing thru it and so it is desirable to regulate this current. The current is often then regulated with a high frequency switching regulator designed for this application using an inductor and capacitor as storage elements and a fly-back diode to re-circulate current between switching cycles.
There is a company that makes a switching regulator integrated circuit (IC) for LED lighting that will accept the high AC voltages directly but the complaint is that they are high priced (due to having no competition at these voltages) and that using them means you will be sole sourced, which is risky from a business standpoint. Another company adapted their power supply IC application designs to show how to produce a power supply for AC to DC with the output current regulated rather than voltage regulated in order to drive a string of LEDs. This is a viable method but once again it is expensive, uses a significant amount of printed circuit board (PCB) space and is sole sourced.
The switching regulator circuits do have an advantage of good efficiency versus most non-switching approaches. In addition, any light flicker will be at the higher switcher frequency rather than the 120 Hz of a linear approach. 120 Hz is not normally visible to the human eye and this is the flicker rate of a standard fluorescent lamp or incandescent lamp. However, switching regulators do have a number of disadvantages that can require additional circuit costs to pass regulatory requirements.
Switchers create high frequency electro-magnetic interference (EMI) that needs to be filtered in order to meet regulations. The AC to DC power supply that is required usually creates harmonic distortion in the current drawn from the power line. This is primarily seen as peak currents much greater than the root-mean-square (rms) current and drawn primarily at the peak of the AC voltage sine wave due to the capacitive current inrush on each AC cycle.
Additional circuitry may be needed to correct the Power Factor (PF) of the lamp to meet regulations. Power Factor is the ratio of real power in watts to apparent power in volt-amps (VA). If the effective load of the LED light is inductive or capacitive then the Power Factor will be less than the ideal 1.0.
In a lighting system using a power supply to produce a DC rail, the PF is typically less than optimum due to the power supply's input and output filter capacitors. These capacitors draw large peak current near the peaks of the input line voltage and much less between peaks. Excessive current peaks cause the peak of the input voltage waveform to be distorted or flattened due to voltage drop in the AC utility service lines. These distortions show up in the voltage and current frequency spectrums of the system as increased odd harmonics. In the usual lighting installation the power supplied is single-phase 120 VAC or 220 VAC connected phase to neutral. In this case the harmonic distortions will be additive on the neutral and can cause the neutral current to be up to 1.73 times greater than the phase current. This can cause the neutral to overheat when the load is within the rating of the service.